Ok, a little background for you to better understand how the collection process. When you owe a debt that you don't pay on time, the clock starts running for the creditor to file a lawsuit to get a judgment on the date starting the date that the payment was due and not paid. That time period is the statute of limitations (SOL) that you see discussed so much in relation to debt. If the creditor files a lawsuit against you within that time period that stops the clock on the running on the (SOL) until the court case is over, e.g. dismissed, a settlement is reached, a judgment rendered. If the creditor sued you, got effective service of process under the applicable state law (which often allows service by publication if you can't otherwise be located to get served) then the creditor may seek a default judgment against you once the time period for you to respond to the lawsuit has expired. As long as the creditor can show the court that it has evidence you owe the debt the court is likely to grant the default judgment.
At that point, the SOL to sue no longer matters. What matters is the length of time the judgment remains in force. States vary in their rules for this but it can be as long as 20 years. Without more information I can't tell you for sure what that time period is. It matters in what state the judgment was recorded, whether you've spent any significant time after the judgment was recorded living outside the state, whether in the time after the judgment was entered you ever obtained a bankruptcy discharge, and perhaps more depending on the details.
The creditor violates the Fair Debt Collection Practices Act (FDCPA) if it threatens to take property/garninsh wages to collect on a consumer debt (if it was a business debt the FDCPA does not apply) when the creditor has no intention to take the threatened actions.
Midland is a company that has been in the collection game a long time as I've seen that name a number of times over the years. It certainly knows the rules. I have no idea the extent to which it follows the rules. It buys up debts that other creditors have given up collecting on their own. So the fact that you have never heard of the company before and never did business with iti before isn't surprising. It is legal for them to buy the debt and step into the creditor's shoes to collect, including enforcing any judgment. If you are getting genuine letters from the local sheriff about potential garnishment/levy of assets then Midland must have had a judgment to show the sheriff. The sheriff doesn't get involved with debt actions until there is a court judgment. How good that judgment is, though, I can't say without seeing and knowing more information.
If you contact Midland or its lawyer they need to provide you with a copy of the judgment if there is one. So I'd start there. I'd also sugget doing some internet searching for judgments against you. Judgments are allowed to remain on your credit report for as long as the judgment is valid. A lot of debt bureaus don't want to bother knowing the judgment lien rules for every state as well as the rules for federal judgment liens so often they'll just drop it after the seven year period it always is allowed to have it on your report. But it wouldn't hurt to get a copy of your credit report (you are given the right to get one report a year for free under federal law) and see if it shows up. If it does, it'll have information that will be useful for you to follow up to learn more about the judgment.
If there is indeed a judgment and it's still valid the creditor can excute on it at any time until the judgment expires. So continue pursuing getting the information you need to determine what your options are. You don't want it to actually reach the point where some enforced collection action is taken.
